Repairing a mouse
A friend of mine asked me to take a look at his laptop mouse, a Genius Navigator 320. It would hang when trying to scroll, and only putting the wheel in a certain position would make it work again. Obviously, it didn't scroll at all.
Since he mentioned something about pressing the wheel (the middle button) to return it to normal operation i thought cracked joints but no go. I replaced the scroll wheel encoder, same thing, so i put the original back in. It did have 4 small lytics but they checked out fine. I actually found a datasheet for the controller in the mouse, it's a PAW3502DL-TK, which makes this a 1200dpi mouse. Not bad... Some measurements showed that when the Z axis pins (the ones reading the encoder) went low, the mouse hung. When any of the two pins were high, the mouse worked. However, tying one of those pins high would kill the scroll functionality, and measurements on a good mouse showed that the controller should work in both states.
More snooping around revealed that pin 4, which is the I/O voltage reference, normally 3.3v, dropped to 1.8v when both Z axis pins went low. Since there was insufficient I/O voltage, it's obvious that the thing stopped working... This pointed to a fault inside the controller chip itself. Unfixable, one might think. Well, there actually was a simple and obvious solution: tie it to the 5v power rail so it no longer drops!
A 100 ohm resistor did the trick. I measured the current drawn by this resistor and it's only 5mA. The operating consumption of this controller is given as 10mA, so that's 50% more, but it's not like 25mW extra would make a difference in battery life when my laptop's CPU has a TDP of 32W, so that's fine. I also tried a 1k resistor and it didn't work, and i was too lazy to try other values. The only difference is that now pin 4 registers 4.7v at all times. Absolute maximum ratings are given as 5.5v for all I/O pins, so it should be fine.
Btw, we ended up finding another laptop mouse lying around at David's place (this guy is David's cousin), so i think i get to keep this one. Sure, this mouse is $10, but nothing beats free and i had nothing to do tonight anyway. And my laptop mouse besides being crappy and low resolution, had a broken cord, so this one comes in handy.
Since he mentioned something about pressing the wheel (the middle button) to return it to normal operation i thought cracked joints but no go. I replaced the scroll wheel encoder, same thing, so i put the original back in. It did have 4 small lytics but they checked out fine. I actually found a datasheet for the controller in the mouse, it's a PAW3502DL-TK, which makes this a 1200dpi mouse. Not bad... Some measurements showed that when the Z axis pins (the ones reading the encoder) went low, the mouse hung. When any of the two pins were high, the mouse worked. However, tying one of those pins high would kill the scroll functionality, and measurements on a good mouse showed that the controller should work in both states.
More snooping around revealed that pin 4, which is the I/O voltage reference, normally 3.3v, dropped to 1.8v when both Z axis pins went low. Since there was insufficient I/O voltage, it's obvious that the thing stopped working... This pointed to a fault inside the controller chip itself. Unfixable, one might think. Well, there actually was a simple and obvious solution: tie it to the 5v power rail so it no longer drops!
A 100 ohm resistor did the trick. I measured the current drawn by this resistor and it's only 5mA. The operating consumption of this controller is given as 10mA, so that's 50% more, but it's not like 25mW extra would make a difference in battery life when my laptop's CPU has a TDP of 32W, so that's fine. I also tried a 1k resistor and it didn't work, and i was too lazy to try other values. The only difference is that now pin 4 registers 4.7v at all times. Absolute maximum ratings are given as 5.5v for all I/O pins, so it should be fine.Btw, we ended up finding another laptop mouse lying around at David's place (this guy is David's cousin), so i think i get to keep this one. Sure, this mouse is $10, but nothing beats free and i had nothing to do tonight anyway. And my laptop mouse besides being crappy and low resolution, had a broken cord, so this one comes in handy.
I will have to admit tho that i've yet to fix a long-term relationship for myself... but i'm working on it. 
Till then, a little bit of this and a little bit of that does the trick.
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